Magneto-resistive memory cell structures with improved selectivity

ABSTRACT

A magneto-resistive memory comprising magneto-resistive memory cells is disclosed, comprising two pinned magnetic layers on one side of a free magnetic layer. The pinned magnetic layers are formed with anti-parallel magnetization orientations such that a net magnetic moment of the two layers is substantially zero. The influence of pinned magnetic layers on free magnetic layer magnetization orientations is substantially eliminated, allowing for increased predictability in switching behavior and increased write selectivity of memory cells.

REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of U.S. patent applicationSer. No. 10/068,465, filed Feb. 6, 2002.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to magneto-resistive memories, andmore particularly, to magneto-resistive memory cell structures thatoffer superior selectivity of memory cells.

[0004] 2. Description of the Related Art

[0005] As computer memory technology advances, magneto-resistive memoryhas emerged as a possible replacement for conventional memory devices.Magneto-resistive memories are non-volatile and employ themagneto-resistive effect to store memory states. These memoriestypically use the magnetization orientation of a layer ofmagneto-resistive material to represent and to store a binary state. Forexample, magnetization orientation in one direction may be defined as alogic “0”, while magnetization orientation in another direction may bedefined as a logic “1”.

[0006] The ability to read stored binary states is a consequence of themagneto-resistive effect. This effect is characterized by a change inresistance of multiple layers of magneto-resistive material, dependingon the relative magnetization orientations of the layers. Thus, amagneto-resistive memory cell typically has two magnetic layers that maychange orientation with respect to one another. Where the directions ofthe magnetization vectors point in the same direction, the layers aresaid to be in a parallel orientation and where the magnetization vectorspoint in opposite directions, the layers are said to be orientedanti-parallel. In practice, typically one layer, the free or “soft”magnetic layer, is allowed to change orientation, while the other layer,the pinned or “hard” magnetic layer, has a fixed magnetizationorientation to provide a reference for the orientation of the freemagnetic layer. The magnetization orientation of the two layers may thenbe detected by determining the relative electrical resistance of thememory cell. If the magnetization orientation of its magnetic layers aresubstantially parallel, a memory cell is typically in a low resistancestate. In contrast, if the magnetization orientation of its magneticlayers is substantially anti-parallel, the memory cell is typically in ahigh resistance state. Thus, ideally, in typical magneto-resistivememories, binary logic states are stored as binary magnetizationorientations in magneto-resistive materials and are read as the binaryresistance states of the magneto-resistive memory cells containing themagneto-resistive materials.

[0007] Giant magneto-resistive (GMR) and tunneling magneto-resistive(TMR) memory cells are two common types of memory cells that takeadvantage of this resistance behavior. In GMR cells, the flow ofelectrons through a conductor situated between a free magnetic layer anda pinned magnetic layer is made to vary, depending on the relativemagnetization orientations of the magnetic layers on either side of theconductor. By switching the magnetization orientation of the freemagnetic layer, the electron flow through the conductor is altered andthe effective resistance of the conductor is changed.

[0008] In TMR cells, an electrical barrier layer, rather than aconductor, is situated between a free magnetic layer and a pinnedmagnetic layer. Electrical charges quantum mechanically tunnel throughthe barrier layer. Due to the spin dependent nature of the tunneling,the extent of electrical charges passing through the barrier vary withthe relative magnetization orientations of the two magnetic layers oneither side of the barrier. Thus, the measured resistance of the TMRcell may be switched by switching the magnetization orientation of thefree magnetic layer.

[0009] Switching the relative magnetization orientations of themagneto-resistive materials in the memory cell by applying an externalmagnetic field is the method commonly used to write a logic state to amagneto-resistive memory cell. The magnitude of the applied magneticfield is typically sufficient to switch the magnetization orientation ofthe free magnetic layer, but not large enough to switch the pinnedmagnetic layer. Thus, depending on the desired logic state, anappropriately aligned magnetic field is applied to switch themagnetization orientation of the free magnetic layer so that themagneto-resistive memory cell is in either a high or a low resistancestate.

[0010] Magneto-resistive memory cells are typically part of an array ofsimilar cells and the selection of a particular cell for writing isusually facilitated by use of a grid of conductors. Thus,magneto-resistive memory cells are usually located at the intersectionsof at least two conductors. A magneto-resistive memory cell is typicallyselected for writing by applying electrical currents to two conductorsthat intersect at the selected magneto-resistive memory cell. Withcurrent flowing through it, each conductor generates a magnetic fieldand, typically, only the selected magneto-resistive memory cell receivestwo magnetic fields, one from each conductor. The current flowingthrough each conductor is such that the net magnetic field from thecombination of both these magnetic fields is sufficient to switch themagnetization orientation of the selected cells. Other magneto-resistivememory cells in contact with a particular conductor usually receive onlythe magnetic field generated by that particular conductor. Thus, themagnitudes of the magnetic fields generated by each line are usuallychosen to be high enough so that the combination of both fields switchesthe logic state of a selected magneto-resistive memory cell but lowenough so that the other magneto-resistive memory cells which aresubject to only one magnetic field do not switch.

[0011] In addition to the two conductors for writing, memory arrays withthree conductors connecting magneto-resistive memory cells have alsobeen developed. The additional conductor may be used exclusively forsensing the resistance of a particular memory cell, allowing anotherconductor to be used exclusively for writing. In this way, writing andreading operations may be performed simultaneously, increasing the speedof data access.

[0012] Magneto-resistive memory technology continues to mature and workcontinues in refining implementation of magneto-resistive memory cells.

SUMMARY OF THE INVENTION

[0013] The preferred embodiments of the present invention providemagneto-resistive memory cell structures which minimize disruptions tothe magnetization orientation of the free magnetic layer caused bypinned magnetic layer magnetic fields. In one embodiment, amagneto-resistive memory cell has an additional pinned magnetic layerand a pinned magnetic layer, with the free magnetic layer and theadditional pinned magnetic layer on either side of the pinned magneticlayer. The additional magnetic layer has a magnetization orientationsubstantially anti-parallel to the magnetization orientation of thepinned magnetic layer. The resulting magnitude of the net magnetic fieldfrom the pinned magnetic layer and the additional pinned magnetic layeris too small to affect the magnetization orientation of the freemagnetic layer or the magnetization orientation of the free magneticlayers of neighboring magneto-resistive memory cells.

[0014] Also provided are methods for constructing the magneto-resistivememory cells of the present invention. In one embodiment, ferromagneticmaterials and the thicknesses of the magnetic layers made from thematerials are first selected such that the magnitude of the magneticfield from one layer is substantially equal to the magnitude of themagnetic field from the other layer. The magnetic layers are thenformed. After formation, the magnetization orientation of each layer isfixed in an opposite direction from the other layer.

[0015] Other features and advantages of the present invention willbecome apparent from the following detailed description, taken inconjunction with the accompanying drawings, illustrating by way ofexample the teachings of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a generalized representation of the magneto-resistivebehavior of a prior art magneto-resistive memory cell;

[0017]FIG. 2 is an additional generalized representation of themagneto-resistive behavior of a prior art magneto-resistive memory cell;

[0018]FIG. 3 is a representation of the magneto-resistive behavior of amagneto-resistive memory cell of the present invention;

[0019]FIG. 4 is a cross-sectional view of one illustrative embodiment ofthe present invention;

[0020]FIG. 5 is a cross-sectional view of another illustrativeembodiment of the present invention; and

[0021]FIG. 6 is a top view of a magneto-resistive memory whichincorporates the present teachings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] To reliably store a state using magneto-resistive memory, it isdesirable to have predictability in switching behavior. As such, it isdesirable to have a magneto-resistive memory cell that will switch to ahigh resistance state by application of a magnetic field of apredictable magnitude and that will also switch to a low resistancestate by application of a magnetic field of a predictable magnitude inthe opposite direction. Moreover, predictability in switching behaviorassociated with a particular applied magnetic field will improve theability to select a particular magneto-resistive memory cell in amagneto-resistive memory cell array. Unfortunately, interactions betweenthe magnetic fields of the pinned and free magnetic layers commonlyfound in prior magneto-resistive memory cells contribute tounpredictability in switching and, thus, undermine the ability toselectively switch cells.

[0023] At short distances on the order of less than about 20 Å, theinteractions of the magnetic fields of two ferromagnetic layers mayinclude either antiferromagnetic or ferromagnetic coupling.Antiferromagnetic coupling tends to cause the magnetization orientationsof the two layers to be parallel, while ferromagnetic coupling tends tocause anti-parallel magnetization orientations. The extent of each typeof coupling oscillates depending, inter alia, on the distance betweenthe two layers.

[0024] Thus, where antiferromagnetic coupling dominates, an appliedmagnetic field must overcome the influence of this coupling to switch afree magnetic layer to the parallel orientation, while the sameantiferromagnetic coupling field will augment an magnetic field appliedto switch the same free magnetic layer to the anti-parallel orientation.Thus, as represented in FIG. 1, the magnitude of the applied magneticfield needed to switch the free magnetic layer to the low resistancestate is increased while the magnitude of the applied magnetic fieldneeded to switch the free magnetic layer to the high resistance state isdecreased. As a consequence, antiferromagnetic coupling fields typicallyincrease the current needed to write the magneto-resistive memory cellto the low resistance state and may cause accidental writing to the highresistance state. In extreme cases, the applied magnetic fields may beinsufficient to overcome the demagnetization fields and the freemagnetic layer may remain in the anti-parallel orientation.

[0025] Alternatively, where ferromagnetic coupling dominates, an appliedmagnetic field must overcome the influence of this coupling to switch afree magnetic layer to the anti-parallel orientation, while these samecoupling fields will augment a magnetic field applied to switch a freemagnetic layer to the parallel orientation. Thus, as represented in FIG.2, ferromagnetic coupling typically increases the power needed to writethe magneto-resistive memory cell to the high resistance state and maycause accidental writing to the low resistance state. In extreme cases,ferromagnetic coupling fields may cause a magneto-resistive memory cellto remain in the low resistance state regardless of the applied magneticfield.

[0026] In less extreme cases, where antiferromagnetic coupling andferromagnetic coupling is strong, but where an applied magnetic field isable to switch the magnetization orientation of the free magnetic layer,the coupling between the free and fixed magnetic layers may still besufficient to cause the magnetization orientation of the free layer toswitch back to its previous orientation. In such cases, depending on thestrength of coupling with the fixed magnetic layer, the orientation ofthe free layer may switch spontaneously, undermining the ability of thecell to be used as a non-volatile memory device. Similarly, less extremeantiferromagnetic coupling and ferromagnetic coupling between the pinnedmagnetic layer of a magneto-resistive memory cell and the free magneticlayers of neighboring magnetoresistive memory cells may causedemagnetization of those neighboring memory cells.

[0027] In addition, manufacturing non-uniformity in the thickness ofnonmagnetic layers separating two ferromagnetic layers, in conjunctionwith the distance related oscillations in the degree ofantiferromagnetic and ferromagnetic coupling, contribute tounpredictability in free magnetic layer switching behavior. Further, therelative influence of antiferromagnetic and ferromagnetic couplingfields on free magnetic layer magnetization may vary among themagneto-resistive memory cells in a magneto-resistive memory array andmay vary between different magneto-resistive memory arrays due tovariations in the patterning steps and/or deposition steps of devicemanufacture. Such variations may lead to unpredictable switchingbehavior and further undermine memory cell selectivity during writeoperations.

[0028] At longer distances, where the distances between magnetic layersare greater than about 20 Å, magnetostatic interactions may dominate. Inthis case, stray magnetic fields originating from the pinned layer mayinteract with and alter the magnetization orientations of the freelayer. Moreover, these stray magnetic fields may interact with themagnetization orientations of free magnetic layers in neighboringmagneto-resistive memory cells, further undermining the switchingpredictability of those memory cells. Magnetostatic interactions are ofparticular concern as work continues on decreasing the distance betweenmemory cells to increase the memory cell density of magneto-resistivememory cell arrays.

[0029] U.S. Pat. No. 6,172,904 discloses one possible structure foraddressing the problem of unpredictable switching behavior caused bypinned magnetic layer and free magnetic layer coupling within aparticular memory cell. That patent describes a structure, illustratedin FIG. 4 of that patent, with a free magnetic layer 4 between twopinned magnetic layers, 6 and 34, with anti-parallel magnetizationorientations M1 and M4. The pinned layers 6 and 34 couple to the freemagnetic layer 4. Thus, coupling to one pinned layer 6 forces themagnetization orientation M3 of the free magnetic layer 4 in onedirection. However, because the structure contains another pinned layer34 with an opposite magnetization orientation M4 and a magnetic field ofthe same magnitude, the second pinned layer 34 also couples to the freemagnetic layer 4. Each pinned magnetic layer 6 and 34 affects the freemagnetic layer 4 in an equal and opposite way, resulting in no nettendency to push the magnetization orientation M3 of the free magneticlayer 4 in any particular direction.

[0030] The preferred embodiments of the present invention takesadvantage of the interactions between two fixed layers to increasepredictability in switching behavior. As represented in FIG. 3, anddiscussed further below, the interactions between the two fixed layersallow for switching behavior in which the magnitude of the appliedmagnetic fields used to switch a magneto-resistive memory cell from alow resistance state to a high resistance state and vice versa aresubstantially equal. Because of this magneto-resistive behavior, themagnitudes of the current used to write a logic “0” or “1” aresubstantially equal, and switching predictability and control isincreased. In addition, the coupling between the free and pinnedmagnetic layers of neighboring memory cells is reduced.

[0031]FIG. 4 is a cross-sectional view of one illustrative embodiment ofthe invention, implemented in the context of a giant magnetoresistive(GMR) memory array. A magneto-resistive memory cell 2 comprises a freelayer 4, a pinned magnetic layer 6, and an additional pinned magneticlayer 8. The pinned magnetic layer 6 has a fixed magnetizationorientation M1, the additional pinned magnetic layer 8 has a fixedmagnetization orientation M2, and the free magnetic layer 4 has aswitchable magnetization orientation M3. While the magnetic orientationsM1 and M2 are shown pointing in particular directions, in anotherembodiment these directions may be reversed, so long as theirmagnetization orientations remain anti-parallel.

[0032] To ensure that a net magnetic moment of the pinned magneticlayers 6 and 8 will not affect the magnetization of the free magneticlayer, the orientations, thicknesses, and materials of the pinnedmagnetic layers 6 and 8 are selected so that the magnitude of themagnetic field of the pinned magnetic layer 6 is substantially oppositeto the magnitude of the magnetic field of the additional magnetic layer8. Because a magnetic field associated with a material may varydepending on the type and quantity of that material, the materials usedand the thicknesses of these materials should be taken into account. Forexample, this may be accomplished by using substantially similarmagneto-resistive materials with a substantially similar thickness foreach pinned magnetic layer 6 and 8 and orienting the pinned magneticlayers 6 and 8 in substantially opposite magnetization directions.Similarly, where the materials comprising each pinned magnetic layerdiffer in the strength of the magnetic field associated with thatmaterial, the respective thicknesses of the pinned magnetic layers 6 and8 may be selected so as to compensate for the different materialsproperties. For example, where the magnetic field associated with thematerial comprising the additional pinned magnetic layer 8 is of agreater magnitude than the magnetic field associated with the pinnedmagnetic layer 6, the thickness of pinned magnetic layer 6 may beincreased to compensate. As such, the net magnetic field from the pinnedmagnetic layers 6 and 8 is too small to affect the magnetizationorientation of the free magnetic layer 4 or a similar free magneticlayer (not shown) in a neighboring magneto-resistive memory cell, inwhich case an applied magnetic field of a particular magnitude canswitch a magneto-resistive cell 2 to the cell's high resistance stateand an opposite applied magnetic field of approximately the samemagnitude can switch the same magneto-resistive cell 2 to the cell's lowresistance state.

[0033] A separating layer 10 preferably separates the pinned magneticlayer 6 from the additional pinned magnetic layer 8. The separatinglayer 10 is preferably comprised of a conductive material that enhancescoupling of the magneto-resistive materials to each other. In thiscapacity, ruthenium or a similar material may be used. The thickness ofthe ruthenium layer should be in a range to allow antiferromagneticcoupling between the pinned magnetic layer 6 and the additional pinnedmagnetic layer 8. Preferably the ruthenium layer is 7-9 Å thick to allowfor the antiferromagnetic coupling.

[0034] In addition, the pinned magnetic layers 6 and 8 are preferablycomprised of ferromagnetic materials, including cobalt, iron-cobalt,nickel iron, nickel-iron-cobalt, or similar material. Where such softferromagnetic materials are used, the magnetization orientation of theadditional pinned magnetic layer 8 is preferably fixed by an adjacentlayer 14 of antiferromagnetic material, in contact with and locateddirectly below the additional pinned magnetic layer 8. Theantiferromagnetic material may be iron-manganese, nickel-manganese,iridium-manganese, platinum-manganese, or similar material. The skilledartisan will appreciate that the anti-parallel configuration of pinnedmagnetic layer 6 and additional pinned magnetic layer 8 allow for use ofantiferromagnetic materials of reduced pinning strength, in comparisonto magneto-resistive memory cells with a single pinned layer. In anotherembodiment, the magnetization orientation of the additional pinnedmagnetic layer 8 is fixed by a layer 14 comprising a permanent magnetmaterial.

[0035] In addition, where the coercivities of the pinned magnetic layer6 and the additional pinned magnetic layer 8 are substantially similar,the adjacent layer 14 may also be useful in the manufacture of themagneto-resistive memory 2. By fixing the magnetization orientation ofthe additional pinned magnetic layer 8 during the manufacturing process,the pinned magnetic layer 6 may be magnetically oriented, withoutsimultaneously changing the magnetization orientation of the additionalpinned magnetic layer 8. The skilled artisan will recognize, however,that an adjacent layer 14 is not necessary to the manufacturing process.For example, simultaneous changing of the magnetization orientation ofthe additional pinned magnetic layer 8 is a reduced concern where thecoercivities of the pinned magnetic layer 6 and the additional pinnedmagnetic layer 8 are not similar, e.g. where the additional pinnedmagnetic layer 8 is formed of a material of higher coercivity than thepinned magnetic layer 6 or where the additional pinned magnetic layer 8is formed of a permanent magnet material.

[0036] As with the pinned magnetic layers 6 and 8, the free magneticlayer 4 is preferably also comprised of a soft ferromagnetic materialsuch as cobalt, iron-cobalt, nickel iron, or nickel-iron-cobalt.

[0037] The free magnetic layer 4 is separated from the pinned magneticlayer 6 by a non-magnetic interlayer 12. In a preferred embodiment, thenon-magnetic interlayer 12 comprises a conductor such as copper to takeadvantage of the giant magneto-resistive effect, where a read currentflows through the conductor of non-magnetic interlayer 12.

[0038]FIG. 5 is a cross-sectional view of another illustrativeembodiment of the present invention wherein like features are referencedby like numerals. In this embodiment, the additional pinned magneticlayer 8 is comprised of a permanent magnet, the orientation of which maybe fixed by exposure to a large external magnetic field. As such, themagneto-resistive memory cell 2 does not require an antiferromagneticlayer 14 to fix the orientation of additional pinned magnetic layer 8.In another embodiment, the additional pinned magnetic layer 8 comprisesa ferromagnetic material with high coercivity such that, in the presenceof applied magnetic fields of magnitudes in a range sufficient to switchthe free magnetic layer, the magnetic moment of this layer isessentially fixed by its intrinsic magnetic anisotropy.

[0039]FIG. 6 is a top view of an illustrative magneto-resistive memory30 that incorporates the present teachings. The magneto-resistive memory30 includes an array of magneto-resistive memory cells, including themagneto-resistive memory cell 2 and additional magneto-resistive memorycells 24-28, each similarly made. Each magneto-resistive memory cell islocated at the intersection of at least two conductors, one each fromthe sets of conductors, 16, 18 and 20, 22.

[0040] The sets of conductors allow reading from and writing to themagneto-resistive memory cells. In one embodiment, conductors 16 and 18are perpendicular to conductors 20 and 22. In other embodiments, theangle 32 formed by conductors 16 and 18 with conductors 20 and 22 mayvary so long as a magnetic-resistive memory cell 2 at the intersectionof two conductors may be selected and switched by a current flowingthrough the conductors.

[0041] While shown forming a rectangular shape, the present teachings donot depend on and, so, do not limit the shape of the magneto-resistivememory cells 2 and 24-28. Further, relative sizes of the conductor lines16-22 and the magneto-resistive memory cells 2 and 24-28 areillustrative only. Here also, the present teachings do not depend onand, so, do not limit the relative sizes of the conductor lines 16-22and the magneto-resistive memory cells 2 and 24-28. Further, whilemagneto-resistive memory cells are typically connected to twoconductors, and are illustrated as such, it will be appreciated thatthis figure only illustrates that, at a minimum, two conductors arenecessary for writing to the memory cell. Additional conductors, e.g. anadditional, separate conductor (sense line) to sense the resistance ofthe memory cell, are not illustrated but can be added. In addition,while the order of each layer relative to other layers should bemaintained, the present teachings do not limit the orientation of thestack of layers as a whole. For example, the stacks illustrated in FIGS.4 and 5 may be constructed on a substrate such that they appear upsidedown relative to the figures.

[0042] Consequently, although this invention has been described in termsof a certain preferred embodiment and suggested possible modificationsthereto, other embodiments and modifications that may suggest themselvesand be apparent to those of ordinary skill in the art are also withinthe spirit and scope of this invention. Accordingly, the scope of thisinvention is intended to be defined by the claims that follow.

1. An integrated circuit comprising a magneto-resistive memory cell, themagneto-resistive memory cell comprising: a free magnetic layer; anon-magnetic interlayer, wherein the non-magnetic interlayer comprises aconductor and is in contact with the free magnetic layer; a pinnedmagnetic layer, wherein the pinned magnetic layer is in contact with thenon-magnetic interlayer; and an additional pinned magnetic layer,wherein the pinned magnetic layer is between the free magnetic layer andthe additional pinned magnetic layer and wherein a magnetizationorientation of the pinned magnetic layer is substantially anti-parallelto a magnetization orientation of the additional pinned magnetic layer,wherein a magneto-resistive material comprising the pinned magneticlayer is different from a magneto-resistive material comprising theadditional pinned magnetic layer.
 2. The integrated circuit of claim 1,wherein the pinned magnetic layer and additional pinned magnetic layerhave preselected thicknesses such that a magnitude of a magnetic fieldof the pinned magnetic layer is substantially equal and substantiallyopposite to a magnitude of an additional magnetic field of theadditional pinned magnetic layer.
 3. The integrated circuit of claim 1,wherein a first magnitude of an applied magnetic field for switching themagnetization orientation of the free magnetic layer in a firstdirection is about 75-125 percent of a second magnitude of an appliedmagnetic field for switching the magnetization orientation of the freemagnetic layer in a direction substantially opposite to the firstdirection.
 4. The integrated circuit of claim 1, wherein the additionalpinned magnetic layer comprises a ferromagnetic material withmagnetization orientation pinned by an adjacent layer.
 5. The integratedcircuit of claim 4, wherein the adjacent layer comprises anantiferromagnetic material.
 6. The integrated circuit of claim 4,wherein the adjacent layer comprises a permanent magnet material.
 7. Theintegrated circuit of claim 1, wherein the pinned magnetic layercomprises a permanent magnet.
 8. The integrated circuit of claim 1,wherein the additional pinned magnetic layer comprises a ferromagneticmaterial with coercivity sufficiently high such that its magnetizationorientation remains fixed in the presence of an applied magnetic fieldof a magnitude sufficient to switch the magnetization orientation of thefree magnetic layer.
 9. The integrated circuit of claim 1, wherein thepinned magnetic layer and the additional pinned magnetic layer areseparated by a separating layer.
 10. The integrated circuit of claim 9,wherein the separating layer is ruthenium.
 11. The integrated circuit ofclaim 1, wherein the nonmagnetic interlayer comprises copper.
 12. Theintegrated circuit of claim 11, wherein the magneto-resistive memorycell is formed within a giant magneto-resistive (GMR) memory array. 13.A method of constructing a magneto-resistive memory cell in anintegrated circuit, comprising: forming a first magnetic layer; forminga non-magnetic interlayer, wherein the non-magnetic interlayer comprisesa conductor; forming a second magnetic layer without forming anothermagnetic layer between the first magnetic layer and the second magneticlayer; forming a first fixed magnetic layer by applying a first magneticfield to fix a magnetization orientation of the first magnetic layer;and forming a second fixed magnetic layer by applying a second magneticfield to fix a magnetization orientation of the second magnetic layer inan opposite direction from the magnetization orientation of the firstmagnetic layer, wherein a magnetic material used in forming the firstfixed magnetic layer is different from a magnetic material used informing the second fixed magnetic layer.
 14. The method of claim 13,wherein a set of ferromagnetic and antiferromagnetic coupling fields ofthe second fixed magnetic layer balance an additional set offerromagnetic and antiferromagnetic coupling fields from the first fixedmagnetic layer.
 15. The method of claim 13, wherein the first magneticlayer and the second magnetic layer have substantially the samethickness.
 16. The method of claim 13, wherein the first magnetic layerand the second magnetic layer are formed sequentially.
 17. The method ofclaim 16, wherein the conductor comprises copper.
 18. A memory devicecomprising a magneto-resistive memory cell, the memory cell comprising:a free magnetic layer; a non-magnetic interlayer, wherein thenon-magnetic interlayer comprises a conductor and is in contact with thefree magnetic layer; a pinned magnetic layer, wherein the pinnedmagnetic layer is in contact with the non-magnetic interlayer; and anadditional pinned magnetic layer, wherein the pinned magnetic layer isbetween the free magnetic layer and the additional pinned magnetic layerand wherein a magnetization orientation of the pinned magnetic layer issubstantially anti-parallel to a magnetization orientation of theadditional pinned magnetic layer, wherein a first magnitude of anapplied magnetic field for switching the magnetization orientation ofthe free magnetic layer in a first direction is about 75-125 percent ofa second magnitude of an applied magnetic field for switching themagnetization orientation of the free magnetic layer in a directionsubstantially opposite to the first direction, wherein amagneto-resistive material comprising the pinned magnetic layer isdifferent from a magneto-resistive material comprising the additionalpinned magnetic layer.
 19. A magneto-resistive memory cell, comprising:a free magnetic layer; a non-magnetic interlayer, wherein thenon-magnetic interlayer comprises a conductor and is in contact with thefree magnetic layer; a pinned magnetic layer, wherein the pinnedmagnetic layer is in contact with the non-magnetic interlayer; and anadditional pinned magnetic layer, wherein the pinned magnetic layer isbetween the free magnetic layer and the additional pinned magnetic layerand wherein a magnetization orientation of the pinned magnetic layer issubstantially anti-parallel to a magnetization orientation of theadditional pinned magnetic layer, wherein a magneto-resistive materialcomprising the pinned magnetic layer is different from amagneto-resistive material comprising the additional pinned magneticlayer.
 20. The magneto-resistive memory cell of claim 19, wherein thepinned magnetic layer and additional pinned magnetic layer havepreselected thicknesses such that a magnitude of a magnetic field of thepinned magnetic layer is substantially equal and substantially oppositeto a magnitude of an additional magnetic field of the additional pinnedmagnetic layer.
 21. The magneto-resistive memory cell of claim 19,wherein a first minimum magnitude of an applied magnetic field forswitching a magnetization orientation of the free magnetic layer in afirst direction is about 75-125 percent of a second minimum magnitude ofan applied magnetic field for switching the magnetization orientation ofthe free magnetic layer in a direction substantially opposite to thefirst direction.
 22. The memory device of claim 18, wherein a separatinglayer separates the pinned and additional pinned magnetic layers. 23.The memory device of claim 22, wherein the separating layer comprisesruthenium.
 24. The memory device of claim 23, wherein the separatinglayer is 7-9 Å thick.
 25. The memory device of claim 18, wherein themagneto-resistive memory cell is located at an intersection of at leasttwo conductors.
 26. The memory device of claim 18, wherein the pinnedand the additional pinned magnetic layers are formed of a materialchosen from the group consisting of cobalt, iron-cobalt, nickel iron andnickel-iron-cobalt.
 27. The memory device of claim 26, wherein amagnetic orientation of the additional pinned magnetic layer is fixed bya layer of antiferromagnetic material.
 28. The memory device of claim27, wherein the antiferromagnetic material is chosen from the groupconsisting of iron-manganese, nickel-manganese, iridium-manganese andplatinum-manganese.
 29. The memory device of claim 26, wherein the freemagnetic layer is formed of a material chosen from the group consistingof cobalt, iron-cobalt, nickel iron and nickel-iron-cobalt.
 30. Thememory device of claim 18, wherein the non-magnetic interlayer comprisescopper.